Depends the potting medium. A higher nitrogen (1st number) fert is recommended for orchids in a bark mix. Even numbers is good for plants in spagh or tree fern. I also use a 'bloom-booster' with higher 2nd and 3rd numbers when plants begin to spike.

I am absolutely contradicting what I have stated for the first 35 years of growing, but studying can pay off, so I believe the 30-10-10 is a better choice because of the relative demand for nitrogen, compared to the other macronutrients, However, that is really not a complete answer, as you are apparently looking for what is best for your plants.

First and foremost, feed frequently, but at VERY low concentrations. An orchid in nature will rarely see a nutrient solution (rainwater cascading through the forest canopy) that is above 15-25 ppm total dissolved solids (TDS), but sees that pretty much any time it rains - daily, in many cases. It makes sense then, that the plants will have evolved to expect such a meager, but frequent food supply. By contrast, if we use 1/2 teaspoon of the 30-10-10 per gallon, we are applying some 200 ppm of nitrogen alone, and a TDS of around 350-400 ppm! Personally, I'd recommend 1/8th teaspoon per gallon twice a week. You're still looking at about 100 ppm TDS or so, but that's a lot less severe than what is currently common.

I always thought we should avoid high-nitrogen fertilizers, as that can stop a plant from blooming, but I have begun to realize that a high-nitrogen diet relates a lot more to the mass of nitrogen applied, and far , far less to the ratio of it to the other nutrients.

Next I'll add that whatever fertilizer you choose, it needs to have plenty of calcium and magnesium in it, as well as all of the other trace elements. Meet those criteria, feed with a low-concentration, frequently-applied regimen, and your plants will thrive.

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